At the beginning of the sixties, the use of aerial means in fighting forest fires to prevent or delay their propagation became widespread, spreading flame retardants, also called fire retardants, specifically on the forest area.
It is known that the typical compositions of fire retardants basically comprise a fire suppressant electrolyte, constituted by salts such as ammonium phosphates and sulfates, viscosity modifiers and pigments.
Due to the ease of transport, flame retardants contain polyphosphates in liquid form and, furthermore, corrosion inhibitors given the corrosive action of the liquid polyphosphates on the components of aluminium or tanks used in the planes.
U.S. Pat. Nos. 3,196,108 and 3,257,316 disclose typical compositions of flame retardants, consisting of aqueous solutions of mono and diammonium salts of the orthophosphoric acid, of a thickening agent such as attapulgite, guar gum or alginates, of colouring agents to improve the visibility of the retardant after it has been thrown and of corrosion inhibitors such as potassium dichromate.
U.S. Pat. No. 3,960,735 disclosed that the tendency of liquid polyphosphates to corrode aluminium was inhibited by the anticorrosive action of ferric ferrocyanide, whereby the component passed to be included as inhibiting agent in the flame retardant composition.
Nevertheless, bearing in mind the environmental impact caused by ferric ferrocyanide, new corrosion inhibitors have been studied, especially additives of the iron ion in its salt forms, such as, for example, pyrophosphates, oxalates and citrates, as disclosed in WO 02/43812.
Despite the advances made in recent years, there is still the need to improve the efficacy of flame retardant compositions used in fire fighting with aerial means.